We modify SAMs by AFM nanolithography, a process by which the surface structure of a SAM is characterized and modified by atomic force microscopy (AFM). To identify flat areas onto which we can easily graft molecules of a different height, we image the matrix (e.g. initial) SAM at the highest possible resolution. The best resolved AFM images are taken at low imaging forces (~0.05nN for thiols) in a liquid cell containing a solution of the molecules to be nanografted.

Under (low) imaging forces, the AFM tip exerts pressure on the order of 107 Pa on the SAM, causing only local deformations. At higher pressures, the SAM becomes disordered and adsorbates are displaced. Above the imaging force that causes displacement of adsorbates, called the "displacement threshold", the image will show the substrate lattice rather than the SAM. If this is done in the presence of a (larger) molecule solution which has, therefore, a higher concentration than the displaced SAM, the new molecules will immediately graft onto the cleared substrate surface. When the displaced area of the matrix SAM has been replaced by the new adsorbates, the modified surface structure can be characterized by scanning at low imaging forces.

Dip-Pen Nanolithography of MHA on Au

Dip-Pen Nanolithography of MHA on Au

Surface Science of Organic Crystalline Surfaces

Why we do this?

Our research focus in the investigation and modification of surfaces composed of organic molecules which have not been extensively investigated with surface science techniques such as; crystalline polymer and self-assembled monolayer surfaces. Current projects of our surface science group include the surface structure, adsorption of molecules, electronic structure of reduced dimensionality and ultrathin film deposition techniques. State-of-the art ultrahigh vacuum equipment is used for the experimental part of the research.

How we do it?

Experimental techniques to research the surface science of organic systems includes angle-resolved photoemission, resonant photoemission, inverse photoemission spectroscopy. Other techniques such as, angle resolved thermal desorption spectroscopy, X-ray photoemission, low energy electron diffraction, scanning tunneling microscopy and atomic force microscopy are also use for a more complete knowledge of these surfaces and their interfaces.

(a), (b), (c) DFT calculation of water layer grown on the Experimental electronic structure of P(VDF-TrFE)